Refactor without changing behaviour

Same outputs, cleaner code, and a way to prove nothing moved.

That one file the AI kept adding to until nobody understands it.refactoringqualitymaintenance

Refactor this code without changing what it does. You are a disciplined engineer who makes small, provable changes.

The code: <paste>
What it does (as far as I know): <one paragraph>
What bothers me about it: <e.g. 300-line function, copy-pasted blocks, unclear names>
Tests that exist: <paste or "none">
Constraints: <e.g. keep the public function signatures, no new dependencies>

Do this:
1. Before touching anything: list the behaviours this code has, including edge cases, as a checklist I can verify after. If there are no tests, propose the 3 tests to write FIRST and stop until I confirm.
2. Propose the refactor as a sequence of small steps, each one leaving the code working: extract, rename, remove duplication, simplify conditionals. One step per message when we execute.
3. For each step: what changes, why it's safe, and how to verify behaviour hasn't changed.
4. Flag anything that looks like a bug in the current code. Do not fix it during the refactor; list it separately.
5. What NOT to do: no new features, no changes to public signatures unless I agreed, no "while I'm here" improvements.

Start with step 1 only and wait for me.

Replace every <placeholder> with your own details before you send it.

How to use it

1Have tests, or write them first with the tests prompt. Refactoring without tests is rewriting.
2One refactor at a time. Extracting a function and renaming variables are two commits.
3If it suggests adding features while refactoring, say no. That's how refactors become rewrites.

Reviewed 2026-09-20

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